While douching is generally discouraged as non-helpful at best or counter-productive at worst, I remember reading a study that found washing the vagina with iodine mostly eliminates all bacteria - desirable and undesirable - but that the beneficial lacto-bacteria are the first to repopulate the cavity.
Quotes and links to two studies about this approach are below.
I recall that when I was looking into the matter, I noticed that Walmart's store brand of iodine wash has that chemical in spermicide that some women are sensitive to. The adjacent bottle of brand-name iodine (Betadine?) doesn't have that chemical. Searching now, it must've been Nonoxynol-9 - https://en.wikipedia.org/wiki/Nonoxynol-9 / https://en.wikipedia.org/wiki/Povidone-iodine
I'll look at my pictures... (EDIT: maybe it's been reformulated: "Active Ingredient: Povidone-iodine, 10%; Inactive ingredients: C12-13, PARETH-9, citric acid, disodium phosphate, glycerin, sodium hydroxide, water" - https://www.walmart.com/ip/Equate-First-Aid-Antiseptic-8-fl-...
This one has Nonoxynol-9: https://www.walmart.com/ip/Betadine-skin-cleanser/46068801
Betadine without Nonoxynol-9: Active Ingredients: Povidone-Iodine (10%) (1% Available Iodine). Purpose: First Aid Antiseptic. Inactive Ingredients: Pareth 25-8, Purified Water, Sodium Hydroxide. - https://www.walmart.com/ip/Betadine-Solution-8-fl-oz/1732500... /EDIT)
tl/dr: use iodine to wipe out all bacteria, so the lactic-acid producing bacteria can repopulate the area.
Two studies that seem to support using iodine washes to take out all the bacteria:
" [...] Contrary to that the lactobacilli counts from patients treated with povidone iodine suppositories decreased after the first week but increased in the second one. Potentially pathogenic germs, e.g. Gardnerella, Bacteroides and Enterobacteria were reduced in a higher extent and with a longer lasting effect after treatment with povidone iodine suppositories than with capsules containing lactobacilli. The results of this study show that native lactobacilli rapidly re-colonize after the antiseptic treatment with povidone iodine. Therefore, there is no need to use lactobacilli in addition." - Efficacy of Povidone-Iodine Vaginal Suppositories in the Treatment of Bacterial Vaginosis - https://www.karger.com/Article/Abstract/57731
"Repeated vaginal washings with 3% H2O2, 15% NaCl and 10% providone iodine were initiated. At the end of each washing, vaginal walls were thoroughly cleaned up with a small gauze. After 10 days of treatment the odor and the vaginal discharge had ceased and 12 months later no relapse had occurred" - Recurrent Bacterial Vaginosis in a Virgin Adolescent: A New Method of Treatment - https://link.springer.com/article/10.1007/s15010-002-2001-9